1. Field of the Invention
The present invention relates to a light emitting device and a method of manufacturing the same, and more particularly, to a light emitting device including one or more grooves formed from a transparent electrode (or an ohmic layer) to a portion of a nitride semiconductor layer, whereby the light efficiency of the light emitting device is improved, and method of manufacturing the same.
2. Discussion of the Related Art
Generally, a light emitting diode (LED) is a kind of semiconductor device that converts electricity into light using the characteristics of a compound semiconductor to transmit and receive a signal or is used as a light source. The light emitting diode generates high-efficiency light at low voltage with the result that the energy saving effect of the light emitting diode is high. Recently, the brightness of the light emitting diode, which was a limit of the light emitting diode, has been considerably improved, and therefore, the light emitting diode has been widely used throughout the whole field of industry, such as backlight units, electric bulletin boards, display units, electric home appliances, and various kinds of automated equipment. Especially, a nitride light emitting diode has attracted considerable attention in the environmentally-friendly aspect because the energy band gap of an active layer constituting the nitride light emitting diode is wide with the result that light emitting spectrum is formed widely from ultraviolet rays to infrared rays, and the nitride light emitting diode does not contain environmentally hazardous materials, such as arsenic (As) and mercury (Hg).
Currently, research is being carried out on a light emitting diode having high brightness that is applicable in various applications. For example, a light emitting diode having high brightness may be obtained by improving the quality of an active layer of the light emitting diode to increase inner quantum efficiency or by assisting light generated from the active layer to be discharged to the outside and collecting the light in a necessary direction to increase light extraction efficiency. Although attempts are being currently made to increase both the inner quantum efficiency and the light extraction efficiency, more active research is being carried out on a method of improving the electrode design, the shape, and the package of the light emitting diode to increase the light extraction efficiency than a method of improving the quality of a semiconductor material to increase the inner quantum efficiency.
The light extraction efficiency is decided by the ratio of electrons injected into the light emitting diode to photons discharged from the light emitting diode. As the light extraction efficiency is increased, the brightness of the light emitting diode is increased. The light extraction efficiency of the light emitting diode is greatly affected by the shape or the surface state of a chip, the structure of the chip, and the package form of the chip. Consequently, it is necessary to pay careful attention when designing the light emitting diode. For a light emitting diode with high output and high brightness, the light extraction efficiency acts as an important factor to decide the light emission efficiency of the light emitting diode. In a conventional method of manufacturing a nitride light emitting diode, however, the light extraction efficiency is limited.
In the conventional nitride light emitting diode, a total reflection condition occurs due to the difference in a refractive index between a nitride semiconductor material and the outside when light generated from an active layer is discharged to the outside. As a result, light incident at an angle more than the critical angle of the total reflection is not discharged to the outside but is reflected into the light emitting diode. Specifically, as shown in FIG. 1, when light generated from an active layer 30 reaches the surface of a nitride semiconductor material 40, the light is not discharged to the outside but is reflected into the light emitting diode if the incident angle of the incident light exceeds the critical angle θc, which is decided by the outer refractive index and the refractive index of the nitride semiconductor material. The reflected light is diminished as the light passes through several channels.
The critical angle is decided by Snell's Law. Specifically, the critical angle may be obtained by Equation 1 below.sin θc=N1/N2  [Equation 1]
Where, θc is the critical angle, N1/is the outer refractive index of the light emitting diode, and N2 is the inner refractive index of the light emitting diode.
The light emitting diode is driven as follows: when voltage is applied to a p-electrode and an n-electrode, holes and electrons move from a p-type nitride semiconductor layer and an n-type nitride semiconductor layer to an active layer. The electrons and the holes are recoupled with each other in the active layer, whereby light is generated from the active layer. The light generated from the active layer advances upward and downward from the active layer. The upward-advancing light is discharged to the outside through a transparent electrode thinly formed on the p-type nitride semiconductor layer. The downward-advancing light is discharged to the outside through a substrate, and is then absorbed into solder used when packaging the light emitting diode, or else, the downward-advancing light is reflected by the substrate, moves upward, and is then reabsorbed into the active layer, or is discharged to the outside through the transparent electrode.
The size of the light generated from the active layer of the light emitting diode is decreased due to absorption and dispersion during the advance of the light in the interior of the light emitting diode. Specifically, the light generated from the active layer of the light emitting diode and to be discharged to the outside through the side of the light emitting diode moves a longer distance than the light to be discharged to the outside through the top of the light emitting diode. For this reason, the size of the light to be discharged to the outside through the side of the light emitting diode is decreased due to the absorption and the dispersion. As described above, the light generated from the active layer of the light emitting diode is totally reflected into the light emitting diode or is absorbed or dispersed during the advance of the light in the interior of the light emitting diode, and therefore, the size of the light is decreased. As a result, the light extraction efficiency of the light emitting diode is lowered.